Generally, multilamp photoflash arrays are constructed to provide sequential operation of a multiplicity of flashlamps. One example of such structures is the so-called "flipflash" as described in U.S. Pat. Nos. 3,894,226 and 4,017,728.
The flipflash unit comprises an elongated planar array of eight high voltage type flashlamps mounted on a printed circuit board with an array of respectively associated reflectors disposed therebetween. The lamps are aranged in two groups of four disposed on the upper and lower halves respectively of the rectangular-shaped circuit board. A set of terminal contacts at the lower end of the unit is provided for activation of the upper group of lamps, while a set of terminal contacts at the top of the unit is operatively associated with the lower group of lamps. The application of successive high voltage pulses (e.g. 2000 to 4000 volts from, say, a piezoelectric source controlled by the shutter of a camera in which the array is inserted) to the terminal contact at the lower end of the unit causes the four lamps at the upper half of the array to be sequentially ignited. The array may then be turned end for end and again inserted into the camera in order to flash the remaining four lamps. In this manner one group of lamps (or half of the array) functions as a flash extender for the other group of lamps so that only the group of lamps relatively farther from the camera lens axis may be flashed. The purpose of such an arrangement is to position the "active" group of flashlamps farther above the camera lens in order to reduce the possibility of a "red-eye" effect that causes the pupils of a person's eyes to appear red or pink in flash pictures taken when the flashlamp is close to a camera lens.
The flipflash circuit board comprises an insulating sheet of plastic having a pattern of conductive circuit runs, including the terminal contacts, on one surface. The flashlamp lead-in wires are electrically connected to the circuit runs by means of eyelets secured to the circuit board and crimped to the lead-in wires. The circuitry on the board includes six printed, normally open, connect switches that chemically change from high to low resistance so as to become electrically conducting after exposure to the radiant energy from an ignited flashlamp operatively associated therewith. The purpose of these switches is to provide lamp sequencing and one-at-a-time flashing. The four lamps of each group are arranged in a parallel circuit, with three of the four lamps being connected in series with respective thermal connect switches. The circuitry on the board further includes a common circuit conductor run which is connected to one lead-in wire of each of the flashlamps in both groups and extends continuously from one end of the circuit board to the other between the common terminal contact at each end of the unit. Initially, only the first of the group of four lamps is connected directly to the high voltage pulse source. When this first lamp flashes, it causes its associated thermal connect switch (which is series connected with the next or second lamp) to become permanently conductive. Because of this action, the second lamp of the group of four is connected to the pulse source. This sequence of events is repeated until all four lamps have been flashed.
The overall construction of the flipflash unit comprises front and back plastic housing members with interlocking means for providing a unitary structure. The front housing member is a rectangular concavity, and the back housing is substantially flat. Sandwiched between the front and back housing members, in the order named, are the flashlamps, a unitary member, preferably of aluminum-coated plastic, shaped to provide the eight individual reflectors of the array, an insulating sheet, a printed circuit board, and an indicia sheet, which is provided with information trademarks and flash indicators located behind the representative lamps and which change color due to heat and/or light radiation from a flashing lamp, thus indicating at a glance which of the lamps have been flashed and not flashed. Each of the individual reflectors has a concave (generally parabolic) surface with the lamps being disposed within this concavity; the rear surface of the reflector has holes or slots to permit light and heat radiation to pass through for actuating circuit board switches and flash indicators. In order to provide electrostatic shielding for the lamps and circuitry, the reflector member is rendered electrically conductive by a reflective metalized coating thereon, and this coating is electrically connected to the common circuit conductor run on the printed circuit board. Further, a metal foil is laminated on the indicia sheet and also connected to this common conductor run of the circuit board.
U.S. Pat. No. 4,164,007 describes an improved multilamp photoflash unit which more efficiently utilizes a given housing volume and thereby reduces the cost of the unit per flashlamp contained therein. More specifically, a compact lamp arrangement is provided whereby additional lamps are contained in a given volume while maintaining light output performance requirements. In a particular embodiment described, ten lamps are provided in a housing having the same dimensions as the above-discussed eight-lamp flipflash unit. This greater compactness is provided by arranging the planar array of lamps in two parallel columns with the tubular envelopes horizontally disposed and with the lamps of one column staggered with respect to the other so that the bases are interdigitated. A pair of reflector panels are aligned with the two columns of lamps and are arranged to overlie the lamp lead-in wires and bases.
Also, U.S. Pat. No. 4,302,794, assigned to the present assignee, describes a more compact, cost-efficient photoflash unit construction comprising a linear array of electrically ignitable flashlamps mounted on a printed circuit board in the form of an elongated strip. The printed circuit strip is located within the longitudinal channel of an elongated housing member having reflective surfaces adjacent to the lamps. A light-transmitting cover panel is attached to the front of the housing member to enclose the flashlamps. The lamps have substantially tubular envelopes and are positioned extremely close to one another with their longitudinal axes substantially parallel to the surface of the printed circuit strip and in substantially coaxial alignment. Typically, the diameter of the lamps, the width of the printed circuit strip, and the width of the channel in the housing member are nearly equal. In order to provide protection against the red-eye effect, a double-ended linear array is described which operates in similar fashion to the aforementioned flipflash. In one specific embodiment, three lamps mounted in the upper half of the printed circuit strip are controlled by a pair of contact terminals at the lower end of the unit, while three lamps in the lower half of the unit are controlled by contact terminals at the top end of the unit. One of the contact terminals for controlling a group of lamps is connected in common to a lead-in wire of each of the lamps of the group, while the other contact is a "hot," or signal, terminal coupled through switching circuitry to the other lead-in wire of each of the lamps. Accordingly, in order to provide an interconnection between the signal terminals at each end of the unit and the respective switching circuitry controlled thereby on opposite halves of the printed circuit strip, respective signal conductor runs must be extended through the respectively inactive halves of the printed circuit strip, respective signal conductor runs must be extended through the respectively inactive halves of the circuit strip. The interconnecting conductor runs from the common terminal contacts are disposed along the outer sides of the circuit-containing surface of the printed circuit board. More specifically, the common circuit run on the bottom half of the circuit board strip is located on the opposite side of the circuit board surface from the common circuit run on the top half of the printed circuit board. As a result, a crossover, or side-to-side connection of the common circuit run is required in order to connect the common terminal at one end of the printed circuit strip with the common circuit conductor run connected to lamp leads in the opposite half of the circuit strip. Such a problem is created by the severe crowding of the conductive paths of this extremely compact unit. The use of printed conductor runs on both sides of the circuit strip with conventional through-connections introduces undesirable cost, e.g., two circuit screening operations are needed together with eyelets, plated-through holes, or the like. A minimum inter-run spacing of about 1.5 millimeters is necessary in order to prevent failure, i.e., promoting electrical sparkover from one run to another at the high voltages used (e.g. 2,000 volts or more).
Also, U.S. Pat. No. 4,286,307, assigned to the assignee of the present invention, sets forth a multilamp photoflash array wherein the ciruit board is in the form of an elongated strip, and the flashlamps are divided into first and second groups of two or more lamps each disposed on respectively opposite halves of the printed circuit strip over the surface containing circuitry. The circuit board and lamps are disposed within the longitudinal channel of an elongated housing member having reflective surfaces adjacent to the flashlamps. The first and second conductor runs comprise a common circuit with the first run connected electrically to one lead-in wire of each of the first group of lamps and the second common circuit run being connected electrically to one lead-in wire of each of the second group of lamps. The printed circuit strip includes first and second connector terminal means at respectively opposite ends, with the first connector-terminal being located on the half of the circuit strip containing the first group of lamps and separated thereby from the second group of lamps, and the second connector-terminal being located on the half of the circuit strip containing the second group of lamps and separated thereby from the first group of lamps. The first common circuit run extends to the first connector-terminal means. A portion of the circuitry couples the first connector-terminal means to each lamp of the second group of lamps and another portion of the circuitry couples the second connector-terminal means to each lamp of the first group of lamps. The first and second groups of lamps are disposed in a linear array, and the channel in the housing member has a cross-section which is substantially semi-rectangular. A continuous coating of conductive reflective material may cover the rear wall and opposite sidewalls of the semi-rectangular channel, and the first and second common circuit runs are respectively disposed parallel and closer to opposite edges of the printed circuit strip facing opposite sidewalls of the channel. The common circuit coupling portion of the circuitry includes the staple which is secured to the circuit board with its center region disposed between the side of the circuit board opposite that carrying the conductor runs and the rear wall of the semi-rectangular channel. In this manner, the center region of the staple can be placed in contact with the conductively coated rear wall of the channel whereby the first and second circuit runs are electrically connected to the conductive reflective coating on the channel walls.
The first and second common circuit conductor runs have respective spaced apart terminations about the midportion of the circuit strip, and the legs of the staple are bent over the conductor-carrying surface of the circuit strip and in contact with respective ones of the terminations of the first and second runs. The circuitry further includes a third conductor run which is connected electrically to the noncommon-connected lead-in wire of one of the lamps and located between the spaced-apart terminations of the first and second runs.
Preferably the housing member is formed of an insulating material and further includes a plurality of segments of reflector cavities formed on opposite sides of the channel, and the unit further includes a light-transmitting cover panel attached to the housing member and enclosing the flashlamps therein. The required crossover connection in this compact array is effectively and inexpensively achieved by use of the conductive, non-corrosive staple as an active, current-carrying segment of the circuitry for carrying lamp-flashing current pulses from the camera socket interface to the lamps in the far end of the array. Wire staples are inexpensive and readily available and provide a simple, rapid manner of implementing circuit run jumpers on ciruit boards. No soldering or other operations are required once the staple is installed on the board.
Additionally, it is known that multilamp photoflash arrays having a connector at opposite ends are available, and one example of such an array is set forth in U.S. Pat. No. 4,051,359. Therein, the array is arranged in a manner to provide upper and lower lamp groups with connectors arranged to energize the lamp group farthest away. Thus, the undesired and known "red-eye" condition is eliminated or at least greatly reduced. Also, the above-mentioned patent sets forth and provides a capability for energization of the closer group of lamps after sequential operation of the furthest lamp group should an operator forget to reverse the array and couple the opposite connector to the energizing source.
Other known techinques for fabricating multilamp photoflash arrays include a process wherein circuit runs are either screen-printed or die-stamped onto a printed circuit board. A screen crossover insulator material is then deposited onto a portion of the circuit runs on the circuit board. Then, a screen-crossover circuit run is printed over the insulator material. Finally, normally open (N/O) switches are screened over the crossover circuit run.
Although the above-described fabrication process has been utilized to provide photoflash arrays, it has been found that problems and non-uniform results tend to arise with such situations and techniques. More specifically, it has been found that a screened-type of crossover insulator configuration requires special materials and special process steps. Unfortunately, solvents and other liquids of the final screening material tend to penetrate the screened insulating material or switch paste whereon the final screening material is deposited. As a result, incomplete conversion of the switches and insulation failures occur which are deleterious to circuit integrity and consistency.
It may be noted that screenable insulators have been fabricated which work very well. However, such structures tend to require not only the above-mentioned special materials which are impervious to the solvents in the materials screened thereon, but also require special and added firing and processing steps. Moreover, it is obvious that such special materials and added processing steps tend to undesirably increase the cost of fabricating the structure.